Gut-friendly bacteria may do more than aid digestion -they could help reduce stress, anxiety, and emotional fatigue, says study.
They are best known for aiding digestion – but probiotics may also influence how you feel. A recent study has found that taking probiotics for just four weeks significantly reduced negative emotions such as anxiety, stress, and fatigue.
The Gut-Brain Connection
Most of us associate probiotics with better digestion. These live bacteria are often found in foods like yoghurt, kimchi, and tempeh, or taken as supplements
But a growing number of studies now point the idea that the gut and brain are constantly in conversation. Through pathways like the vagus nerve, immune responses, and hormonal signals, the gut microbiome play a part in influencing how we feel.
This connection is at the heart of a new study published in npj Mental Health Research, led by researchers Dr Katerina Johnson and Dr Laura Steenbergen. It found that probiotics may help reduce negative emotions, including stress, anxiety, and fatigue, when taken consistently over a few weeks.
Daily Surveys Could Detect Mood Changes
The researchers recruited healthy young adults and gave them either a probiotic supplement or a placebo. The probiotic blend included common strains like Lactobacillus and Bifidobacterium.
To better capture subtle emotional shifts, participants in the study were asked to report how they felt every day. By tracking how participants rated their moods daily, the researchers picked up subtle yet consistent mood improvements among those on probiotics.
Previous studies on probiotics and mental health have often produced mixed results, possibly since they relied on standard psychological questionnaires.
“It is striking that by simply asking participants how they were feeling each day, we could detect the beneficial effects of probiotics on mood,” says Steenbergen. In contrast, standard psychological tests were less sensitive and unable to pick up these subtle changes.
Not Quite a Replacement for Antidepressants
It took about two weeks for the probiotics to start making a difference. And while the change was noticeable, the researchers are clear: probiotics are not a replacement for antidepressants.
Whereas antidepressants can flatten both negative and positive emotions, probiotics in this study only reduced negative mood, leaving positive emotions unaffected. This suggests a gentler modulation of emotional state.
Still, the researchers made it clear that probiotics do not replace antidepressants or professional mental health treatment.
Who Might Benefit the Most?
Interestingly, those with risk-averse tendencies – people who naturally avoid uncertain situations -experienced a greater improvement in mood.
Probiotics also seemed to subtly enhance participants’ ability to recognise emotional facial expressions, suggesting changes in emotional processing.
What Does This Mean for Mental Health?
The idea that probiotics could be used to support mental health is still very much in early stages. Many questions remain unanswered about how exactly these probiotics work as well as their long-term effects.
The researchers suggested they could be explored in future as a potential early intervention, especially to prevent negative emotional states from worsening over time.
The study also makes a compelling case for researchers to look beyond complex tests and embrace simpler tools like daily mood tracking in psychological research.
As Johnson and Steenbergen note in their paper: “Sometimes the most simple questions reveal the most meaningful answers.”
External References
- Johnson, K.VA., Steenbergen, L. Probiotics reduce negative mood over time: the value of daily self-reports in detecting effects. npj Mental Health Res 4, 10 (2025). https://doi.org/10.1038/s44184-025-00123-z
